1. Field of the Invention
The present invention relates in general to an apparatus for converting outline data representative of an outline of an image such as a letter, a symbol and a graphical representation, into dot data representative of dots to be formed to reproduce the image. More particularly, the present invention is concerned with improvements in such a data converting apparatus.
2. Discussion of the Prior Art
Images such as characters including letters and symbols represented by image data are printed, displayed or otherwise reproduced according to the image data suitably processed by a computer. Commonly, the image data takes the form of dot data indicating whether a dot should be formed in each of picture elements which are the smallest part of picture image and which determine the resolution of the reproduced image. If a batch of dot data representative of all the images available for reproduction is prepared and stored in an image data memory such as a character data memory, the memory should have an extremely large storage capacity. It is therefore desirable to store a batch of outline data representative of the outlines of the images such as the characters, and convert the outline data into the corresponding dot data by suitable data converting means, when the images are printed, displayed or otherwise reproduced, as disclosed in Japanese Patent Publication No. 53-41017.
In the data converting means disclosed in the above publication, the outline data is defined in a coordinate system in which picture elements are defined by a plurality of parallel scanning lines parallel to one of the X and Y axes. For example each stoke of a character is defined by the picture elements (referred to as "outlining picture elements") within which are located intersections between the character outline and each scanning line. The bits of the dot data corresponding to these outlining picture elements are all set so as to indicate the dots to be formed in the corresponding outlining picture elements. These bits are referred to as "dot-forming bits". Then, the bits of the dot data corresponding to the picture elements (referred to as "internal picture elements") which are surrounded by the outline defined by the outlining picture elements are all set as the dot-forming bits.
This known data converting apparatus is thus adapted to implement two steps for preparing a necessary batch of dot data, i.e., a first step for obtaining the dot-forming bits for the outlining picture elements, and a second step for the dot-forming bits for the internal picture elements. Moreover, the known apparatus requires that the second step be conducted such that the logical value of the bits are set one after another for the individual internal picture elements. In other words, the apparatus requires determination for each of a large number of bits of dot data corresponding to a large number of outlining and internal picture elements arranged along each scanning line, in order to check if each bit is a dot-forming bit or not. The bits are set so as to indicate the absence of dots to be formed (i.e., the absence of any part of the character to be reproduced), until a first dot-forming bit for an outlining picture element is detected along the relevant scanning line. The bits between the detected first dot-forming bit and a second dot-forming bit for another outlining picture element are all set so as to indicate the dots to be formed, namely, set as the dot-forming bits for the internal picture elements. The bits following the detected second dot-forming bit for the second outlining picture element are set so as to indicate the absence of dots to be formed, until a third dot-forming bit for a third outlining picture element is detected along the relevant scanning line. The bits following the detected third dot-forming bit are also set as dot-forming bits for another group of internal picture elements. Therefore, the known data converting apparatus is not a sufficiently efficient apparatus, requiring a comparatively long data processing time for checking each of the bits for each scanning line, in order to determine whether the bit should be a dot-forming bit or not.